This invention relates to antennas, phased array antennas, and specifically to a phased array antenna utilizing planar phase shifter or true time delay (TTD) devices and a structure for embedded control and bias lines.
Phased array antennas offer significant system enhancements for both military and commercial SATCOM and radar systems. In the military scenario it is crucial to maintain near total situational awareness and a battle brigade must have reliable satellite communications in a moving platform environment. Maintaining connectivity in these environments is critical to future systems such as the Future Combat Systems (FCS) and other millimeter wave SATCOM and radar systems. The application of these technologies to satellite communication subsystems will provide high-directionality beams needed to close the link with reasonably sized power amplifiers and will provide excellent anti-jam (A/J) and low probability of detection and interception (LPD/LPI) performance.
It is well known within the art that the operation of a phased array is approximated to the first order as the product of the array factor and the radiation element pattern as shown in Equation 1 for a linear one-dimensional array. A similar expression to Equation 1 exists for a two-dimensional array 10 arranged in a prescribed grid as shown in FIG. 1.                                           E            A                    ⁡                      (            θ            )                          ≡                                                                              E                  p                                ⁡                                  (                                      θ                    ,                    ϕ                                    )                                            ︸                                                                        Radiation                                                                              Element                                                                              Pattern                                                              ⁢                                                                      [                                                            exp                      ⁡                                              (                                                  -                                                      j                                                                                          2                                ⁢                                π                                ⁢                                                                                                                                  ⁢                                                                  r                                  o                                                                                            λ                                                                                                      )                                                                                    r                      o                                                        ]                                ︸                                                                                  Isotropic                                                                                        Element                                                                                        Pattern                                                                        ·                                                                                ∑                    N                                    ⁢                                                            A                      n                                        ⁢                                          exp                      ⁡                                              [                                                                              -                                                          j                                                                                                2                                  ⁢                                  π                                                                λ                                                                                                              ⁢                          n                          ⁢                                                                                                          ⁢                          Δ                          ⁢                                                                                                          ⁢                                                      x                            ⁡                                                          (                                                                                                sin                                  ⁢                                                                                                                                          ⁢                                  θ                                                                -                                                                  sin                                  ⁢                                                                                                                                          ⁢                                                                      θ                                    o                                                                                                                              )                                                                                                      ]                                                                                            ︸                                            Array                ⁢                                                                  ⁢                Factor                                                                        Equation        ⁢                                  ⁢        1            
Standard spherical coordinates are used in Equation 1 and θ is the scan angle referenced to bore sight of the array. Introducing phase shift at all radiating elements 15 within the array 10 changes the argument of the array factor exponential term, which in turns steers the main beam from its nominal position. Phase shifters are RF devices or circuits that provide the required variation in electrical phase. Array element spacing, Δx or Δy of FIG. 1, is related to the operating wavelength and sets the scan performance of the array 10.
To prevent beam squinting as a function of frequency, broadband phased arrays utilize true time delay (TTD) devices rather than traditional phase shifters to steer the antenna beam. Expressions similar to Equation 1 for the one- and two-dimensional TTD beam steering case are readily available in the literature.
Conventional waveguide phased array technology in which planar microwave/millimeter wave circuitry is used to implement phase shifting or true time delay (TTD) circuits is illustrated in FIG. 2. A basic unit cell 20 features a microstrip, coplanar waveguide or slot line transition for a rectangular waveguide 21 designed to operate in the fundamental TE10 mode in FIG. 2. A planar circuit board to waveguide transition 22 is typically located in the center of the waveguide 21 where the electric field (E field) strength is at its maximum to facilitate coupling between the waveguide 21 and the planar circuit to waveguide transition 22. A packaged phase shifter or TTD device 25 is located on the planar circuit to waveguide transition 22. Several phase shifter architectures as well as TTD devices compatible with planar RF circuits can be used in this architecture, as shown in the table below. The table is a non-exhaustive list of TTD and of phase shifter devices 25 that may be used in the unit cell 20 of FIG. 2.
TechnologyActive DeviceCircuit ArchitectureTTDMEMsSwitched LineTTDMMIC SemiconductorVector ModulatorOptical TTDFuture TechnologyTBDPhase ShifterMMIC Semiconductor/PINSwitched Line, Loaded Line,diode, Ferrite MicrostripHigh Pass, Low Pass,Reflective Hybrid
The traditional waveguide-to-printed circuit transition approach shown in FIG. 2 has several shortcomings. There must be a robust, continuous RF ground connection between the planar circuit board 22 and the waveguide 21 broad wall to ensure low loss and consistent RF performance. This is very difficult to accomplish with conventional extruded waveguide technology since the circuit board 22 is somehow slid inside and secured to the waveguide 21. It is difficult to bring in control lines for the phase shifter/TTD device 25 from the exterior of the waveguide 21 without affecting RF performance. For large arrays, the assembly of this architecture is costly because many circuit boards 22 are individually mounted with one circuit board 22 in each radiating element waveguide 21. For large one-dimensional and two-dimensional phased array antenna assemblies, the routing and connection of bias control lines is very cumbersome.
What is needed is a cost-effective, low weight, high performance realization of one-dimensional and two-dimensional waveguide phased array antennas that utilize planar phase shifter or true time delay circuitry featuring embedded control and bias lines.